In chromatography, samples to be analyzed are held in a sample vial having a rubber septum. To inject the sample held within the vial into a chromatograph for analysis, a syringe is used. The needle of the syringe is used to pierce the rubber septum. A sample is then withdrawn and subsequently injected into a chromatograph. Most often, this is an operation performed manually by a technician. This has proven to be inefficient and inaccurate, and not satisfactory for the standards of today.
Therefore, there have been attempts to automate this process. These attempts to automate the process have often resulted in complex mechanical systems. Chromatography inherently requires very accurate quantities of sample. These small, very precise quantities have been difficult to achieve in automated systems. Very accurate and reproducible control of the plunger is critical to chromatography, and is difficult to accomplish in an inexpensive automated system.
These difficulties have been compounded by the need to incorporate syringes that are not precisely manufactured into the automated system. The syringes, being relatively inexpensive, have manufacturing tolerances that vary. One of these variances is in the location of the plunger when it is fully depressed to the plunger stop prior to the withdrawing of the sample. Often, an automated plunger drive mechanism tends to overdrive the plunger stop, destroying the syringe.
Therefore, there is a need for a simple plunger homing mechanism that permits different syringes manufactured within a relatively large tolerance range to be inserted into an automated chromatography system, capable of accurately and reproducibly withdrawing a sample of a very precise volume from a sample vial.